Age-based life cycle traits of the broadclub cuttlefish Sepia latimanus confirmed through release−recapture experiments

Abstract

To understand the age-based life cycle traits of the broadclub cuttlefish Sepia lati- manus, we obtained biological information about the species through releaserecapture experi- ments, where 166 345 hatchlings with markings in their cuttlebones were released into their nat- ural habitat of Ishigaki Island, southern Japan, and 96 adult cuttlefish were recaptured over 2 successive years. Age groups were determined based on 3 indices: the number of lamellae in the cuttlebone, dorsal mantle length (DML), and the collection date of wild cuttlefish. The length- frequency data of DML, reconstructed from 4340 cuttlebones collected from either a fish market or coastal beaches, were analysed over a period of 3 yr. The cuttlefish consisted of 2 age groups (0 yr and 1 yr), and each group is thought to die after maturation at the end of the spawning season, indicating that they are different breeding groups. The ratio of 1 yr cuttlefish to total cuttlefish was highest at the beginning of the breeding season (November) and gradually de - creased throughout the breeding season. Abundance, maturation, and mating conditions of each breeding group and the estimated hatching season of cuttlefish in the wild suggest that the 0 yr and 1 yr groups contribute equally to production of offspring early in the hatching period, while the contribution of 0 yr cuttlefish is larger later in the hatching period. Offspring hatched later may return as recruits to breed as 1 yr cuttlefish the following year. Our analysis highlighted that the population of broadclub cuttlefish is composed of 2 breeding groups with alternative short and long life spans. This is the first study in which the life cycle traits of a Sepia species have been successfully clarified with releaserecapture experiments.